There are only 2 companies using FRP walls on RV cargo style trailers that I am aware of W&P and Renegade, a truck based motor coach manufacturer that also builds matching trailers. There is one manufacturer of regular semi trailers with FRP, and that is Great Dane, who makes them for specialty uses, chemical companies and for hauling batteries.
My 34FK starting rotting at many of the fasteners at the top of the wall, some leaked some don't.
Mine is a 2007 that resided with the 1st owner in western PA from 2007 - 2013. I have had it all over the eastern half of the country since. The rot was evident when I bought it and the price reflected it.
Even with it's problems I still like the trailer, it is built exceptionally strong and has exactly what I need, although it is definitely a 3 season trailer.
If you can keep it under cover while not being used the rot situation will not occur fast enough to be a problem.
There are other full aluminum cargo trailers with living quarters. Race car guys use them. That is the only alternative, but probably more expensive.